The present invention relates to a mechanical amplification mechanism for amplifying a motion of electromechanical transducer elements. More particularly, the invention relates to a mechanical amplification mechanism which amplifies a displacement by employing either elecrostrictive or piezoelectric elements as a driving source and which is principally used for printing means and switches.
A mechanical amplification mechanism of this kind has been used especially as a printing means of a printer and switches of a relay, etc. In recent years, a printing mechanism has been considered in which power dissipation and the quantity of heat generation are reduced by employing either electrostrictive or piezoelectric elements as a driving source. This mechanism is capable of high-speed operation. In this mechanism, it is necessary to amplifiy the slight displacement of the piezoelectric elements (e.g. 0.005 mm-0.01 mm) so that a sufficient printing needle stroke can be obtained for the printing mechanism (about 0.5 mm).
To this end, a piezoelectrically driven printing mechanism is shown and described in the U.S. Pat. No. 4,193,703 entitled "Matrix Printer with Piezoelectrically Driven Printing Needles." This patent was issued to Walter Sakmann on Mar. 18, 1980. In the mechanism of this patent, both ends of a buckling spring are fixed to holding elements. One of these elements is seated on a piezoelectric crystal device and the other is seated on a fixed holding portion. The buckling spring is deflected by exciting the piezoelectric crystal, to drive a printing needle which is attached to the central part of the buckling spring.
In such a mechanism, depending on deflecting the buckling spring, however, the magnitude of deflection .delta. of the central part of the buckling spring is geometrically approximated to ##EQU1## where .epsilon. denotes the displacement of the piezoelectric crystal and l the length of the buckling spring. Assuming that .epsilon.=0.01 mm by way of example, it is not possible to make .delta.=0.5 mm unless l=60 mm. Moreover, a force acts on the fixed holding portion due to the elongation of the piezoelectric crystal. The fixed holding portion is deformed to open outwardly, so that the displacement to be transmitted to the buckling spring 6 suffers a loss. After all, the length of the spring must be 100 mm or greater. Accordingly, this structure has the disadvantage that the size of the printing mechanism becomes large.
To solve this problem, I have previously described a mechanical amplification mechanism which is disclosed in U.S. patent application Ser. No. 593,981. In this mechanism, two lever arms are fixed to both ends of a piezoelectric element. These arms extend at a right angle to the expanding and contracting direction of the piezoelectric element. Free ends of those two arms hold a band spring therebetween. The band spring has an acting element such as a printing needle or switch terminal at its central portion. The two lever arms are rotatably supported at a fulcrum locating between their fixed end and their free end. Accordingly, the two lever arms turn around the fulcrums by an expansion of the piezoelectric element, so that their free ends approach each other. As a result, the two lever arms bend the band spring, thus causing the acting element to be driven in the direction perpendicular to the expanding direction of the piezoelectric element.
According to this mechanism, the expansion of the piezoelectric element is amplified by the lever arms and the band spring. Therefore, a sufficient acting element stroke (about 0.6 mm) which is necessary for a printer head or a relay can be obtained by a small-sized mechanism. However, this mechanism still has the disadvantage that the piezoelectric element may be broken during the operation of the two lever arms because those lever arms impose bending forces upon the piezoelectric element, with the force acting in the direction perpendicular to the expanding direction, when the arms are turned.